A rotary output beam corrector conventionally comprises a casing in which an electric motor is mounted. This motor, associated with a speed reducing transmission, drives the output element of the device, in the form of an output shaft projecting from the casing of the device.
This output shaft has a male or female profiled element such as a hexagonal head or socket, which enables the output shaft to be coupled to a threaded control rod which is engaged in a fixed thread secured to the housing of the headlight and in engagement with the reflector of the latter. In this connection, rotation of the output shaft of the corrector causes the control rod to turn and also, by virtue of its screw thread, to be displaced in straight line movement (or translation) so as to cause the reflector to pivot about a fixed point. In this way the orientation of the headlight beam is adjusted. Such adjustment generally consists of horizontal adjustment as a function of variations in the attitude of the vehicle, but it is also possible to envisage azimuth adjustment if desired.
One problem encountered in this type of beam corrector lies in the fact that it has to be associated with additional means for carrying out manually, usually in the factory, adjustment of the reflector so as to put the beams into a reference position or so-called zero position. It is accordingly from this zero position that the electrical correcting device will operate in order to make the running adjustments that become necessary when the vehicle is in use.
The manual zero adjusting means generally consist of a mechanical system located outside the casing of the corrector, and having an adjusting knob accessible from outside and coupled, through suitable means such as cranks, meshing toothed wheels or the like with the output side of the corrector, so as to enable a geometrical parameter of the coupling between the output shaft of the electrical corrector and the control rod of the reflector to be varied. These means are often complicated and difficult to fit, due to the need for fitting both an electrical corrector and a manual corrector, and they increase the selling price of the headlight.